Single sideband modulator



March 8, 1960 D. K. WEAVER, JR

SINGLE SIDEBAND MODULATOR Filed Dec. 1'7, 1956 f TEE 2 Sheets-Sheet 1 VJ; J6

Maj.

March 8, 1960 D. K. WEAVER, JR 2,928,055

SINGLE SIDEBAND MoDULAToR 2 Sheets-Sheet 2 Filed Deo. 17. 1956 NNN B,11B, each having their center tap connected through secondary windings10C, 11C to an adjustable tap on corresponding resistances 10D, 11D. Theoutside terminals of windings 10B, 11B and resistances 10D, 11D areconnected together through diodes which are poled as indicated. Thus, inthe case of modulator 10, these aforementioned outside terminals areconnected together by diodes 10E and 10F and also by diodes 10G and10i-1 forming a conventional ring or balanced modulator. Likewise, inthe case of modulator- 11, diodes 11E, 11F, 11G and 11i-l are providedfor the same purpose. 1t is noted-that the diodes 10E and 10G areserially connected and also the diodes 10F and 10H are seriallyconnected `for passage of current in the same direction.

These secondary windings 10C and 11C introduce, respectively, a co-sineand a sine term of an audio frequency signal developed in the audiofrequency oscillator 36, through corresponding primary windings 38 and39.

The oscillator 36 has its grounded terminal connected to theinterconnected cathodes of the amplifier tubes 40 and 41. The otherterminal of oscillator 36 is connected through a phase shifting network42 to the control grids of these tubes 40 and 41. More specifically, theungrounded terminal of oscillator 36 is connected to the control gridsof -tubes 40 and 41 through condenser '44 and resistance 45,respectively; and, these two control grids are interconnected byresistance 46 and condenser 47 which have their junction point grounded.A source of voltage 50 has one of its terminals grounded and the otherone of its terminals connected to corresponding anodes of tubes 40 and41 through primary windings 38 and 39, respectively. The signals thusdeveloped through multiplication or modulation across the resistances10D and 11D, respectively, are applied to the Vlow pass filters 14 andl15 through connections which involve a resistance serially connectedwith a coil serving as isolation between the balanced modulation and thelow pass filter. More specifically, these connections involveresistances 10], 10K, 11] and 11K.

The low pass filters 14 and 15 are conventional and include Seriesconnected coils 10L, 10M, 11L, 11M, 14A, 14B, 14C, 14D, 15A, 15B, 15Cand 15D, as well as shunt connected condensers 14E, 14F, 14G, 14H, 15E,15P, 15G and 15H. It is noted that lthe junction point of condensers14G, 14H, as well as the junction point of vcondensers 15G, 15H, aregrounded to preserve a balanced condition with respect to ground. Thesecond or radio frequency modulator stages 16, 17 are of identicalconfiguration as the previously described modulator stages 12 and 13.

Thus, in like manner, modulator stage :16 includes serially connecteddiodes 16E, 16G and serially connected diodes 161? and 16H, as well asthe tapped output resistance 16D and secondary winding 16C. Similarly,the modulator stage 17 includes the serially connected diodes 17E, 17G,the serially connected diodes 17F, 17H, the tapped output resistance 17Dand the secondary winding 17C.

'These secondary windings 16C and 17C serve to introduce into thecorresponding modulators 16 and 17 a co-sine and a sine term of a radiofrequency signal developed in the oscillator stage 60 through primarywindings 68 and 69, respectively, which are tuned to the radio frequencysignal by corresponding condensers 63A and 69A.

`The radio frequency oscillator 60 has one of its terminals grounded andthe other one of its terminals connected through a phase splittingnetwork 72 to control grids of corresponding amplifier tubes 80 and 81.More specifically, the ungrounded terminal of oscillator 60 is connectedto the control grid of tube 80 through condenser 84 and to the controlgrid of tube 81 through 4 resistance 85. These control grids areinterconnected by the serially connected resistance 86 and condenser 87which have their junction point connected to the grounded cathodes oftubes and 81. A voltage source 90 has one of its terminals grounded andhas its positive terminal connected to the anodes of tubes 80 and S1through corresponding tuned coils 68 and 69.

The Signals developed by multiplication or modulation across theresistances 16D and 17D are combined by serially connecting thesecondary windings and 101, having associated primary windings 102 and103. The

Vwinding 102 is connected to the outside terminals of resistance 16Dthrough resistances 104 and 106, and such winding 102 is shunted by botha condenser 108 and a resistance 110. Likewise, the primary winding 103is connected to the outside terminals of resistance 17D ,throughresistances 105 and 107, and such winding 103 is shunted by both acondenser 109 and a resistance 111. The signals thus combined or addedby windings 100 and 101 are applied to the linear amplifier 31, havingits output terminal connected to transmitting antenna 32.

With reference to Figure 2, the following are representative values forthe designated components: The diodes are crystal diodes `of the 1 N 100type. The resistances 10D and 11D each have a value of 750 ohms. Theresistances 10J, 10K, 11] and 11K each have a resistance of 375 ohms.The coils 10L, 10M, 11L and 11M have a value of 27.5 millihenries. Thecoils 14A, 14C, 15A and 15C each have a value of 100 millihenries. Thecoils 14B, 14D, 15B and 15D each have a value of 75 millihenries. Thecondensers 14E and 15E each have a value of 0.15 microfarad. Thecondensers MF and 15P each have a value of 0.20 microfarad. Thecondensers 14G, 14H, 15G and 15H each have a value of 0.11 microfarad.The resistances 16D Land 17D each have a value of 1500 ohms. Theresistances 104, 106, 105 and 107 each have a value of 750 ohms. Thecondensers 108 and 109 each have la value of 3000 micromicrofarads. Theresistances 110 and 111 each have a value of 2000 ohms. The coils y102and 103 each have a value of 8.5 microhenries. The resistances 45 and 46may each have a value of 10,000 ohms. The condensers 44 and v47 eachhave a value of .01 microfarad. The resistances 85 and 86 each have avalue of 160 ohms. The condensers S4 and 87 each have a value of 1000rnicro-microfarads.

The single side band signal thus developed and transmitted using thearrangement specically shown in Figure 2 may be received and detected bycoventional radio receivers which have provisions for receiving anddetecting single side band signals.

It is noted that each `one of the balanced modulators 10, 11, 16 and 17is a double balanced modulator and sometimes referred to in the art as aring modulator. Such modulator, of course, includes nonlinear elementsso that when two signals are applied thereto, sum and differencefrequencies are developed, but the ling modulator functions so that thetwo signals applied thereto are balanced with respect to the output.This means that the output of each balanced modulator comprises both ordouble side bands of the signals combined in the modulator. In order toassure balanced operation, adjustable taps are provided on the variousresistances 10D, 11D, 16D and 17D. Thus, each of the balanced modulatorsmay be referred to as a signal multiplying and suppressing meanssensitive to signals applied thereto for developing only side bandcomponents thereof. The output of each of the balanced modulators thuscomprises a double side band signal. The function of the lter orfrequency selective means `14 and 15 is generally that of selecting oneof the double side bands so that a single side band signal is applied asan input to the balanced modulator stages 16 and '17. However, in thissystem the lower side band which is selected by low pass filters 14 and15 is folded about zero frequency and hence 1 width, W, as the originalsignal e,(T).

" asesinas? band. Double side band signals resultV from the application-of the Vtwo signaliEU)V and E2G) kto balanced modulators 16, 17 andsuch signals Vhave the same' band- By combining the signals at theoutput of stages 16 the resulting signal e(T) also has a bandwidth W.YHowever, the various responding; quadr'aturecompcnentursaidthirdsignal,:ands4 vme" 'combiningfthe outputsof each-of thelast-mentioned' indivi ual' means.

2.'.ln'a systemvof the character described, asg'nal com-A prising a bandof audio frequencies, a pair of substantially? identical channelsv Afed"by said signal, each one Vof said channelscomprising, in'cascade, afirst balanced modulaspectrum components either add or cancel so that asingle side lband signal VappearsV at `tl1e output' ofthe other stage f16A, 17A.

quate suppression of the higher frequency components The lowestfrequency of these unwanted products occurs at Zwo- W/.Z radians perfrom thebalanced modulators.

second which provides Va transition region from fW/ 2 to 2w0-W/2. Thesetwo filters 14 and 15 should have identical response characteristicsinthe pass band. The two signals E1(.t) and E20) are applied to anotherpair of balanced modulators 16 and 17. In this latter instance, thetranslating frequency wc is the band center of the single side bandsignal. The location ofthe normal carrier is at wc-wo radians Ipersecond. The output fromthese two balanced modulators 16, 17 are addedtogether, forming the single side band signals. Any high frequencycomponents centered `about multiples of we are eliminated by passing thesame through a Vfrequency selective network or filter. By interchanginge1(t) with eo(t) and wo with we, the block 'diagram of Figure Yl becomesthe lblock diagram for a single side band demodulator.

Indeed, in accordance with ano-ther aspect of the present invention,Vthe receiving system incorporates a detection system illustratedgenerally in Figure l, as modified above, and illustrated morespecifically in Figure 3. This transformation indicated aboveinlconnection with Figure l is illustrated in the block diagram of ythereceiver in Figure 3. The signal e0(t) at the receiver may be directlyreceived on the antenna 132 and amplified before being applied to thebalanced modulator stages 1-12, y113; or such signal represented by'e(t) may be produced by conventional superheterodyne action using alocal oscillator, as indicated in the stage 133. The signal e0(t) iscombined with quadrature components of the signal having a frequency ofl megacycle andV corresponding to wc. The output of each of themodulator stages -112 and L13 is a double side band signal, land 'thelower side band of each of the signals is selected by the correspondingfrequency selective or filter net-work 114, 115, so that a single sideband signal is applied .to the balanced modulator stages 116, 117, towhich is also applied quadrature components of the signal having afrequency of 1800 cycles per second corresponding to wo. The output;V ofthe modulator stages 116, 117 is combined in the adder stage 116A,1117A, and the output of the last-mentioned 1' tor] frequency selectivemeans and a second balanced modulator, said signal being 'applied'to therst modulator in each-channel, a secondi audio signal having individualquadrature components applied to the first modulator incorrespondingchannels, said secondfaudio signal 'having a-friequencyIinsaid band of audio frequencies, a'second Y signal having individualquadrature components applied to-the'second modulator'in correspondingchannels, and means combining the output of the second modulator in oneof said channels -with the output of the second modulator in the otherone of said channels.

n3. In a system of the character described, a source of a first signalvoltage having a frequency band, a source of a secondsignal voltagehaving a frequency within said band, a source of a third signal voltage,balanced modulator means coupled to said rst and Second sources andfunctioning to produce first side band signals in accordance with, onthe one hand, said first signal and a quadrature component of saidsecond signal, and, on the other hand, second side band signals inaccordance with said first signal and a second quadrature component ofsaid second signal, frequency selective means for filtering said firstand second side band signals, second balanced modulator means coupled tosaid third source and receiving said filtered side band signals andfunctioning to Vproduce third side band signals in accordance with oneof said filtered side band signals and a quadrature component of said.third signal and functioning to produce fourth side` band signals inaccordance with the other filtered side band signals and a secondquadrature component of saidV stage is amplified in the audio amplifier120 before being applied to the speaker 122.

I claim:

l. In a system of the character described, a rst signal comprising aband ofk audio frequencies, a second signal of audio frequency withinsaid band, a third signal of radio frequency, individual meansmultiplying said first signal with individual quadrature components ofsaid second signal to derive individual side band signals cor respondingrespectively to each one of said components, individual frequencyselective means for selecting a portion of each of said side bandsignals, individual means multiplying a corresponding one of saidportions with a corthird signal, 'and means combining said third andfourth side band signals.

v4. In a system of the character described, a first signal having a bandof frequencies, a second signal having a frequency within said band,means deriving quadrature components of said second signal, individualsignal multiplying and suppressing means sensitive to said first signaland a corresponding one of said quadrature components and functioning todevelop first and second side bandV signals, first and second frequencysel-ective means for filtering respectively said first and second sideband signals, a third signal, second individual multiplying andsuppressing means sensitive to corresponding filtered side band signalsand respectively corresponding quadraturel components of said thirdsignal, and means combining the output of said second signal multiplyingand suppressing means. n

5. In a system of the character described for producing a single sideband suppression carrier signal, the combination comprising Aa firstsignal comprising a band of audio frequencies, a second signalcomprising itwo, quadrature components and having a frequency withinsaid band, a third signal comprising two quadrature components, firstindividual balanced modulating means sensitive to said `first signal andcorresponding quadrature components of said second signal andfunctioning to develop first and second side brand signals, Secondindividual balanced modulating means sensitive respectively to saidfirstl and second side band signals and corresponding quadraturecomponents of said third signal and functioning to develop third andfourth side band signals, and means combining said third land fourthside band signals to produce a single sideband signal.

6. In a method of the character described, the steps comprisingmultiplying a first band o-f signals with quadrature components of asecond signal within said band to develop first and second side bandsignals, filtering said first and second side band signals to producethird and fourth signals which are each only the lower side bands ofsaid iii-st and second signals, multiplying said third and fourthsignals respectively with quadrature components of a fifth signal todevelop third and fourth side band signals, and combining said third andfourth side band signals.

7. In a system of the character described, a pair of substantiallyidentical channels connected in parallel, a first source of signals in aband of frequencies fed into one end of each of said channels insubstantially the same phase, each of said channels comprising incascade first balanced modulating means, low pass filtering means, andsecond balanced modulating means, an adding network receiving the outputof the second balanced modulating means in each channel, a second sourceof signals hav-ing quadrature components thereof supplied to the firstbal- 15 anced modulating means in corresponding ones of said pair ofchannels, said first and second source of signals having a comparablefrequency ofthe same value within said band of frequencies, said lowpass filter in each channel passing only the lower side band of signalsin corresponding channels.

Rcferences Cited in the ile of this patent UNITED STATES PATENTS1,719,052 Green July 2, 1929 l,964,522 Lewis lune 26, 1934 2,018,356Hammond Oct. 22, 1935 2,173,145 Wil-kier Sept. 19, 1939

